Here are some details on Apple's patent listed with their RAND claims in the
W3C's now-finalized SVG standard:
http://www.delphion.com/details?&pn=US05379129__
US5379129: Method for compositing a source and destination image using a
mask image
Jan.Â 3,Â 1995
Here is the summary:
This invention provides a method for compositing a source image and a
destination image using a mask image to produce a result image in a digital
image processing system. The method is, on a pixel-by-pixel basis, using
the mask image to select between the source and destination images: where a
black color value for a mask pixel selects the color value of the
corresponding pixel of the source image; and a white color value for a mask
pixel selects the color value of the corresponding pixel of the destination
image; and where an intermediate color value for a mask pixel selects a
weighted average between source and destination pixel color values. The
calculations of the weighted average color value are done in color space,
such as on a color component by color component basis. The result image can
be displayed or stored for further use. This method can be described in
boolean expression according to the formula:
result=((1-mask)*source)+(mask*destination).
So this is an example of the worst kind of patent: a patent on a mathematical
expression. Furthermore, a particularly obvious one that many, including
myself, have been using for years prior to the date of Apple's patent.
Words fail me at this point. Please draw your own conclusions.
--
Daniel